Receiver for time division multiplex system without explicit time slot assignment

ABSTRACT

A technique for a time division multiplex system in which access to shared broadcast communication media is granted on a demand basis. Particular connections are assigned slot times at the transmitter based on demand. However, no specific information regarding the assignment of time slots need be communicated to the receivers. The transmit side employs a forward error correction technique followed by multiplication by a cover sequence unique to each connection. All receivers listen to the broadcast transmission channel all of the time. The receiver assigned to each connection decodes the signals in such a manner that only the receiver with the correct cover sequence assigned to a particular connection will successfully decode the data associated with that connection. Data frames that fail the forward error correction process are discarded, and only those frames which are successfully decoded are passed up to a higher layer. The occurrence of an erroneously received frame is not necessarily always reported to the transmit side of the connection; only a packet level error indication is made. In this way, information containing time slot assignment need not be communicated between the transmitter and receiver, and yet data will be correctly received.

BACKGROUND

Continued growth in the electronics and computer industries, and indeedgrowth in the economy in general, is increasingly attributed to thedemand for access to the Internet and myriad of services and featuresthat it provides. The proliferation in the use of computing equipment,both of the conventional desk top variety as well as of the portablevariety, including laptop computers, hand-held Personal DigitalAssistants (PDAs), Internet enabled cellular telephones and other accessdevices have resulted in a corresponding increase in demand for networkinfrastructure.

The access points into the Internet are, however, mostly provided viacommunication systems that were originally intended for carryingnon-data traffic. For example, the Public Switched Telephone Network(PSTN) is still heavily used as a dial-up access point for many home andpersonal users. Although there are emerging various standards thatprovide higher speed access points, these emerging technologies, as wellas older high speed technologies such as TI and/or fractional TIservices still make use of the telephone network. The telephone networkwas, unfortunately, optimized to carry voice traffic as opposed to datatraffic. In particular, these networks were intended to supportcontinuous analog communications, as compared to the digitalcommunication protocols needed for Internet packet-orientedcommunications.

For example, voice grade services typically require access to acommunication channel bandwidth of approximately 3 kilohertz (kHz).While techniques do exist for communicating data over such radiochannels at a rate of 9.6 kilobits per second (kbps), such low bandwidthchannels do not lend themselves directly to efficient transmission ofdata at the typical rates of 56.6 kbps or higher that are now commonlyexpected.

In addition, the very nature of Internet traffic itself is differentfrom the nature of voice traffic. Voice communication requires acontinuous duplex connection, that is, a user at one end of a connectionexpects to be able to transmit and receive to a user at the other end ofa connection continuously, while at the same the user at the other endis also transmitting and receiving.

Usage patterns of the Internet are also quite different from voicecommunications. For example, consider that access to Web pages over theInternet in general is burst-oriented. Typically, the user of a remoteclient computer first specifies the address of a Web page to a browserprogram. The browser program at the client computer then sends therequest as a Transmission Control Protocol (TCP)/Internet Protocol (IP)message packet, which is typically about 1000 bytes in length, to anetwork Web server. The Web server then responds by sending the contentof the requested Web page, which may include anywhere from approximately10 kilobytes to several megabytes of text, image, audio or video data.Because of delays inherent in the network, and because the Internet issuch a vast interconnected mesh of networks, users experience delays ofseveral seconds or more for the requested web page to be routed to them.The user may thereafter spend several seconds or even several minutesreading the contents of the page before specifying a next page to bedownloaded.

The result is that a typical Internet connection remains idle for arelatively long period of time. However, once a request is made, theuser expects the information to be transmitted to the client at arelatively rapid rate. An additional difficulty is provided in wirelessaccess systems in that there are typically many more potential users orsubscribers than the available number of physical radio channels.Therefore, making wireless channels available only on an instantaneous“as needed” basis makes sense, and indeed is a requirement if wirelessdata transfer services are to efficiently operate. Thus, dynamic trafficchannel allocation schemes are one way to increase the efficiencywireless data communication systems in an effort to more efficientlyutilize available channel resources.

Some type of demand-based multiple access technique is thereforetypically required to make maximum use of the available wirelesschannels. Multiple access is often provided in the physical layer, suchas by Frequency Division Multiple Access (FDMA) or by schemes thatmanipulate the radio frequency signal such as Time Division MultipleAccess (TDMA) or Code Division Multiple Access (CDMA). In any event, thenature of the radio spectrum is such that it is a medium that isexpected to be shared. This is quite dissimilar to the traditionalenvironment for data transmission, in which a wired medium such as atelephone line or network cable is relatively inexpensive to obtain andto keep open all the time.

SUMMARY OF THE INVENTION

A particular problem occurs in existing communication systems that useon-demand multiple access techniques to permit multiple users to share aphysical channel. Due to the nature of Internet communications, thesetechniques increasingly make use of Time Division Multiplex (TDM) toassign time slots to specific users or connections on a demand basis. Insuch a system, time slot assignments are communicated to a receivereither explicitly or implicitly.

In an implicit assignment system, time slots are preassigned in a fixedpattern. Therefore, receivers know when to listen for data intended forthem. However, implicit assignment systems are typically not flexibleenough to efficiently handle Internet traffic.

In an explicit assignment system, time slots are assigned to specificusers on a demand basis by a central system controller. Information asto which time slots are assigned to which connection is then explicitlycommunicated from the central controller to each remote unit. Theoverhead associated with transmitting information as to time slotassignment is therefore information bandwidth that otherwise cannot beallocated to transmitting payload data.

Unfortunately, this situation is exacerbated in a wireless communicationenvironment in which additional radio channels must be allocated forcommunicating such time slot assignment information. This is aparticularly acute problem on a forward link direction of such systems,that is in the direction from the network towards the user. MostInternet traffic is typically communicated in the forward direction.

The present invention seeks to overcome these difficulties.Specifically, the invention is used in a Time Division Multiplex (TDM)communication system where a physical radio communication channel, whichmay be defined by CDMA codes or in other ways, is shared among multipleusers or connections through the use of time slots. Time slots areallocated on a demand basis. For example, a given radio channel in aforward direction is allocated only for a pre-determined time slotduration and only as needed by specific connections.

The invention overcomes certain disadvantages of prior art systems. Inorder to minimize overhead in the allocation of time slots to specificusers, no specific time slot assignment information needs to becommunicated to the receiver. However, time slot assignment may still bemade on a demand basis.

This is accomplished through the use of a particular coding scheme atthe transmitter, and a particular protocol at the receiver. The transmitcoding scheme takes a data packet and divide it into sub-packets orframes. The frames are separately assigned to time slots at thetransmitter, driven by connection demand. Each given frame is firstencoded by a Forward Error Correction (FEC) code which may typically addadditional bits to the frame. A user specific cover sequence, which may,for example, be a pseudonoise (PN) sequence, is added to the frame data.The FEC encoded frame is then assigned a time slot and transmitted overthe shared radio channel.

At the receiver end of the connection, all receivers always attempt toreceive to all frames in all time slots. As part of this receivingprocess, each receiver applies its specific assigned cover sequence inorder to attempt to receive each frame. The candidate frame is thensubmitted to an inverse FEC decoding process to attempt to properlydecode each frame.

A process within a first layer of the receive protocol, which may beimplementation access layer, handle the candidate frame as follows. If aframe is properly decoded, as indicated by the FEC decoding processbeing successfully completed, the frame is passed up to the next higherlayer of the receiver protocol. However, if a frame is erroneouslydecoded, it is simply discarded. Most importantly, the discarded frameevent does not cause any error indication to be returned to a higherlayer of the protocol.

The result is that only the receivers having the correct cover sequenceassigned to them will properly decode frames intended for them. Anyframes decoded that are not intended for that particular receiver willtherefore normally be discarded.

A higher layer of the receive protocol then takes care of the problem oferroneously discarded frames intended for the receiver and/orerroneously accepted frames that were intended for other receivers.Specifically, the higher layer protocol may determine, from informationcontained in a frame such as a sequence number, when such frame has beenerroneously discarded or erroneously accepted. Only at this higherlayer, which may be a link layer of the protocol, will a receiver issuean error indication back to the transmitter, requesting re-transmissionof the packet.

There are several advantages to this arrangement.

First, only cover code information, and not time slot information, needsto be made available at each receiver. Therefore, the overheadassociated with dynamic assignment and deassignment of time slots tospecific receivers, such as the need to transmitting information as totime slot assignment and deassignment is eliminated.

Second, the system works especially well where the system has wirelesscommunication or other multiple access techniques, such as Code DivisionMultiple Access (CDMA), to define the physical channels. Eliminating theneed to transmit time slot information from the transmitter to thereceiver provides for much greater flexibility on demand assignment ofindividual channel resources. Reducing signaling overhead demand in suchsystems also increases the amount of information bandwith available forcarrying payload data, while decreasing the amount of channelinterference, thereby increasing capacity of the system as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a communication system in which access isgranted to a shared communication medium on a time division multiplexbasis, without explicit time slot assignment information being madeavailable to the receivers.

FIGS. 2A and 2B are more detailed diagrams of the transmitter encodingand receiver decoding.

FIG. 3 illustrates the format of a packet and the frames containedtherein.

FIG. 4 is a flowchart of the operations performed by a lower layerprotocol at the receiver.

FIG. 5 is a flowchart of the operations performed by a higher layerprotocol at the receiver.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is a block diagram of a communication system 10 that makes use ofTime Division Multiplexing (TDM) to allow multiple transmitters andreceivers to share access to a common channel resource on a time slotbasis, without the need for explicit time slot assignment information tobe made available at the receiver. In the following description, thecommunication system 10 is described such that the shared channelresource is a wireless or radio channel. However, it should beunderstood that the techniques described here may be applied to allowshared access to other types of media such as telephone connections,computer network connections, cable connections, and other physicalmedia to which access is granted on a demand driven time slot basis.

The communication system 10 includes a number of Personal Computer (PC)devices 12-1, 12-2, . . . 12-h, . . . 12-1, corresponding SubscriberAccess Units (SAUs) 14-1, 14-2, . . . 14-h, . . . 14-1, and associatedantennas 16-1, 16-2, . . . 16-h, . . . 16-1. Centrally located equipmentincludes a base station antenna 18, and a base station processor (BSP)20. The BSP20 provides connections to an from an Internet gateway 22,the Internet 24, and network file server 30. The system 10 is a demandaccess, point to multi-point wireless communication system such that thePCs 12 may transmit data to and receive data from network server 30through bi-directional wireless connections implemented over forwardlinks 40 and reverse links 50. It should be understood that in a pointto multi-point multiple access wireless communication system 10 asshown, a given base station processor 20 typically supportscommunication with a number of different subscriber access units 14 in amanner which is similar to a cellular telephone communication network.

The PCs 12 may typically be laptop computers 12-1, handheld units 12-h,Internet-enabled cellular telephones or Personal Digital Assistant(PDA)-type computers. The PCs 12 are each connected to a respective SAU14 through a suitable wired connection such as an Ethernet-typeconnection.

An SAU 14 permits its associated PC 12 to be connected to the networkfile server 30. In the reverse link direction, that is, for data traffictraveling from the PC 12 towards the server 30, the PC 12 provides anInternet Protocol (IP) level packet to the SAU 14. The SAU 14 thenencapsulates the wired framing (i.e., Ethernet framing) with appropriatewireless connection framing. The appropriately formatted wireless datapacket then travels over one of the radio channels that comprise thereverse link 50 through the antennas 16 and 18. At the central basestation location, the BSP 20 then extracts the radio link framing,reformatting the packet in IP form and forwards it through the Internetgateway 22. The packet is then routed through any number and/or any typeof TCP/IP networks, such as the Internet 24, to its ultimatedestination, such as the network file server 30.

Data may also be transmitted from the network file server 30 to the PCs12, in a forward direction. In this instance, an Internet Protocol (IP)packet originating at the file server 30 travels through the Internet 24through the Internet gateway 22 arriving at the BSP 20. Appropriatewireless protocol framing is then added to the IP packet. The packetthen travels through the antenna 18 and 16 to the intended receiver SAU14. The receiving SAU 14 decodes the wireless packet formatting, andforwards the packet to the intended PC 12 which performs the IP layerprocessing.

A given PC12 and the file server 30 can therefore be viewed as the endpoints of a duplex connection at the IP level. Once a connection isestablished, a user at the PC 12 may therefore transmit data to andreceive data from the file server 30.

As will be described in greater detail later, the reverse link 50actually consists of a number of different types of logical and/orphysical radio channels including an access channel 51, multiple trafficchannels 52-1, . . . 52-t, and a maintenance channel 53. The reverselink access channel 51 is used by the SAUs 40 to send messages to theBSP 20 to request that traffic channels be granted to them. The assignedtraffic channels 52 then carry payload data from the SAU 14 to the BSP20. It should be understood that a given IP layer connection mayactually have more than one traffic channel 52 assigned to it. Inaddition, a maintenance channel 53 may carry information such assynchronization and power control messages to further supporttransmission of information over the reverse link 50.

Similarly, the forward link 40 typically includes a paging channel 41.The paging channel 41 is used by the BSP 20 to not only inform the SAU14 that forward link traffic channels 52 have been allocated to it, butalso to inform the SAU 14 of allocated traffic channels 52 in thereverse link direction. Traffic channels 42-1 . . . 42-t on the forwardlink 40 are then used to carry payload information from the BSP 20 tothe SAUs 14. Additionally, maintenance channels carry synchronizationand power control information on the forward link 40 from the basestation processor 20 to the SAUs 14.

Additional information as to one possible way to implement the variouschannels 41, 42, 43, 51, 52, and 53 is also provided in PatentCooperation Treaty Application No. WO99/63682 entitled “Fast AcquisitionOf Traffic Channels For A Highly Variable Data Rate,” assigned toTantivy Communications, Inc. and published Dec. 9, 1999.

The traffic channels 42 on the formal link 40 are shared in a TimeDivision Multiplex scheme among a number 8 the SAUs 14. Specifically, atypical forward link traffic channel 42 is partitioned into apredetermined number of periodically repeating time slots 60-1, 60-2, .. . 60-5 for transmission of messages to the multiple SAUs 14. It shouldbe understood that a given SAU 14 may, at any instant in time, havemultiple time slots 60 assigned to it or at other times may have no timeslots at all assigned to it.

The allocation of time slots occurs on a demand basis among the variousSAUs 14 in a physical area serviced by the system 10. The time slotassignments are typically determined by the Base Station Processor (BSP)20 which is coordinating the assignment of resources to specificconnections between users of the computers 12 and servers 30. Theseassignments are made based upon a number of factors, such as trafficdemand, requested quality of service, and other factors.

The manner of assignment of a specific time slot 60 to a specific one ofthe SAUs 14 is not of importance to the present invention. Rather, thepresent invention is concerned with the manner in which a receiver suchas a SAU 14 may correctly receive time slotted data on the forward linkwithout having available to it. Specific information as to which timeslots are assigned to other SAUs 14.

More particularly, refer now to FIGS. 2A and 2B where there is shown ageneralized block diagram of the encoding process at the transmit sideand decoding process at the receive side according to the invention. Itshould be understood that in accordance with the notation of FIGS. 2Aand 2B, a transmitter 100 may, in the case of the forward link 40, bethe Base Station Processor (BSP) 20 shown in FIG. 1. Likewise, thereceivers 130 shown in FIGS. 2A and 2B are one or more of the SAUs 14shown in FIG. 1.

At the transmitter 100, a packet containing the data to be transmittedto a specific receiver i (D_(i)) is first fed to a framer 102. Theframer 102 divides the packet into sub-packets or frames. The number ofbytes in each of the frames, and the number of frames per packet, andthe packet size is not of particular importance to the presentinvention. Any number of techniques can be used to determine the optimumframe size and number of frames per packet.

In any event, the framed data is then fed to a Forward Error Correctionencoder (FEC) 104. The FEC encoder 104 takes the framed data and addsadditional bits to permit error detection at the receiver 130. Anynumber of FEC encoder processes may be used such as BCH codes, blockcodes, turbo codes, turbo product codes and the like.

The FEC encoded frame is then fed to a cover sequence circuit 106. Thecover sequence modulator 106 applies a cover sequence, C_(i) associatedwith the particular end-to-end connection that is to receive the dataD_(i). A number of different cover sequences C are associated with eachof a number of different connections that can be carried over the sharedbroadcast media 120. The cover sequences C_(i) may be any suitablesequence. For example, one class of such sequences are the longpseudorandom raise (PN) sequences. In such an instance, the coversequence is applied by module-2 multiplication of the cover sequenceC_(i) with the data D_(i). Suitable cover sequences may also includeother near-orthogonal sequences that scramble the data. The coversequence selected should scramble the data sufficiently to cause the FECdecoder 134 to fail to decode it properly if an incorrect cover sequenceis applied at the receiver.

It should be understood then that the coded signals output from a numberof transmitters 110 may then be applied to a time division multiplexer115. Thus, output from a number of transmitters 110-1 . . .110 i . . .110 t may be fed as input to the TDM multiplexer 115 to assign timeslots of the multiplexal signal 118 to particular ones of thetransmitters 110. The time division multiplexed signal 118 is then fedover the shared broadcast media 120, to the receivers 130, which in thepreferred embodiment is the forward link 40 described in FIG. 1.

A specific exemplary receiver 130-1 consists of a cover sequence circuit132, an FEC decoder 134, and frame error detect 136. More specifically,the cover sequence circuit 132 applies the cover sequence C_(i)associated with a particular receiver 130 to the signal that itreceives. For example, consider the case of the receiver 130-i, which isthe intended recipient for data sequence D_(i). In order to properlyreceive the data D_(i), cover sequence C_(i) is fed to the respectivecover sequence demodulator 132-i. In the case of using long PN codes,the cover sequence circuit performs a modulo-2 multiplication by thecover sequence. Other types of cover sequences may require differentprocessing. In any event, the output of the cover sequence demodulator132-i is thus the same signal 105 that was presented to the input of thecorresponding sequence modulator 106 in the transmitter 110-i.

The cover sequence signal 133-i is then applied to the FEC decoder 134-ito remove the FEC encoding applied at the transmitter 100. The result isa digital signal or set of bits that represents the input frame whichwas output by the framer 103 at the transmitter 110-i.

An error detect is then performed in block 136 to determine whether ornot the received frame was received properly. In case that it was, theframe is marked as “passing” and then passed up to a higher lever packetassembler 150. The pocket assembler 150 will be described in greaterdetail in FIGS. 3-5.

In the normal course of processing (i.e., when no bit errors areexperienced in transmission), only a single receiver 130-i which is theintended receiver will receive a pass indication from the output of theframe error detect 136. The other frame error detectors 136-1, 136-2, .. . 136-i−, 136-i-i+1, . . . , 136-R detect will, in the normal courseof events, receive a fail indication. This is because only the receiver130-i (having associated with it the cover sequence C_(i) which was usedto encode the data at the transmitter 110-i) will cause proper output atthe cover sequence demodulator 132-i. The other cover sequence circuits132-1, . . . 132-i−1, 132-i+1, . . . , 132-R will scramble the receiveddata such that the FEC decoder will request an error. Therefore, theframe error check process 136 associated with such other receivers willnormally indicate that the frame detection failed.

Turning attention now to FIG. 3, the framing format for an exemplarydata packet D_(i) will be described prior to discussing the operation ofthe packet assembler 150 in detail. A packet 151 is divided intomultiple frames 152-1, 152-2 . . . 152-M . . . 152-X at the transmitter110. An exemplary frame 152-2 consists therefore of a section of payloaddata 166 taken from the packet 151 and additional information includingat least a packet identifier field 162, a packet length field 163, asequence number field 164, a Cyclic Redundancy Check (CRC) field 16.

A packet identifier 162 associated with each frame 152 indicates theparticular packet with which the frame 152 is associated. The packetlength field 163 indicates the length of the packet. The sequence numberfield 164 is a number indicating the particular order that the frame152-2 occupies in the specific packet 151. For example, the sequencenumber within the frame 152-2 (being the second frame F2 in the packet151) would be a binary representation of the number “2.”

FIG. 4 is a flow chart of the operations performed by the packetassembler 150 at a lower level layer of a protocol at the receiver 130.This protocol may typically be considered to be part of a link layerprotocol that is responsible for assembling and properly detectingframes, as opposed to properly detecting the bits of each frame.

In a first step of this process, a given receiver 130-i determines whichcover sequence, C_(i), is associated with it. This information may beprovided to the receiver 130-i on a paging channel 141 associated withthe forward link, such as when the base station processor 20 initiallysets up a connection between a particular subscriber access unit 14 andthe server 30.

In other embodiments, the cover sequence C_(i) can be pre-assigned tothe particular receiver 130-i, such as during a system configurationprocess.

In any event, once activated, the receiver 130-i enters a state 210 inwhich it is continuously receiving bits of the frames. Upon receipt of acomplete frame, the process previously described for receiver 130-i isperformed, including the cover sequence circuit 132, FEC decoding 134,and frame error detect 136.

If, in state 212, the frame error detect 136 indicates that a frameerror has occurred, then processing proceeds to state 214 in which theframe is discarded. However, not only is the frame discarded at thispoint, but it should be noted that no error indication is provided to acorresponding link layer back at the originator of the frame such as atthe server 30, or to a higher layer at the receiver 130.

Back in state 212, if the frame was received without error, processingcontinues to state 216 in which the frame is passed up to a higher layerprotocol at the receiver associated, for example, with the packetassembler 150 process.

FIG. 5 shows a flow chart of the steps performed by the packet assembler150 to further complete the process according to the invention. Uponreceipt of a frame, in state 240, a state 242 is next entered in whichthe frames are assembled to complete a packet. In state 244, if this isnot the last frame of a packet, such as indicated by comparing the framelength information and the sequence number information in the packet,then processing returns to state 240. The process then continues, withthe packet assembler 150 continuing to receive frames.

In state 244, which is entered upon an indication that the last framehas been received, then state 248 is entered in which it is determinedwhether or not a frame is missing. This determination can be made byexamining the frame sequence numbers associated with each packet todetermine if a frame is missing. Returning to FIG. 3, there may, forexample, be in an assembled set of frames 152-1, 152-2, . . . 152-x,with a particular frame 152-m which is still missing at the time framethe last frame 152-x is received. This missing frame, F_(m), can be due,for example, to errors which occur during transmission which caused itto be erroneously discarded by the frame error check process 136.

In any event, if there is a missing frame 152-m, then a state 250 isentered in which retransmission of the missing frame is requested. Atthis point, an error notification message is sent back to theappropriate higher level layer at the server 30. This higher level layermay, for example, be a network layer, a transport layer, or otherprotocol layer above the link layer.

From state 248, if there are no frames missing, but if an extra frame orout of sequence frame is received, such as again may be determined bycomparing the packet identifier information 162 associated with eachframe 152, then a state 252 is entered. In state 252, the out of orderframe is discarded.

If there are no extra frames, that is, if all of the frames received doappear to be associated with a particular packet, then the packet hasbeen properly received and it may be passed up to yet another, higherlayer of the receiver protocol.

It should be understood that the steps 244, 248 and 252 may be performedin any particular order. For example, missing frame determination may bemade before the last frame is received and/or out of order frame orframe associated with an incorrect packet determination may also be madebefore either of the other two determinations.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A method for communication in a time divisionmultiplexed system wherein access to a shared physical channel isassigned on a demand basis by allocating timeslots to provide multipleconnections between transmitters and receivers, each given connection ofthe multiple connections having a given receiver, the method comprising:at a transmitter, allocating at least one time slot to carry forwardlink packet data on a forward link channel; a dividing a given packetinto at least one frame; encoding each of the at least one frames with aforward error correction code; further cover sequence encoding each ofthe at least one frames with a cover sequence unique to the givenconnection between the transmitter and the given receiver; at the givenreceiver, performing a cover sequence decoding process by combining areceived signal with a cover sequence unique to the given receiver ofthe given connection, to provide a candidate frame, and decoding thecandidate frame using a forward error correction decoding process, thecover sequence encoding operable to be decoded only by the coversequence unique to the given receiver corresponding to the givenconnection.
 2. A method as in claim 1 additionally comprising: if theforward error correction decoding process indicates a correctly receivedcandidate frame, then forwarding the candidate frame to a packetassembler process in a higher level communication layer.
 3. A method asin claim 1 additionally comprising: if the forward error correctiondecoding process indicates an erroneously received candidate frame,discarding the candidate frame without passing any error indication to ahigher level communication layer.
 4. A method as in claim 1 wherein theshared physical channel is a wireless channel.
 5. A method as in claim 1wherein the cover sequence is provided to the given receiver during asystem configuration phase.
 6. A method as in claim 1 wherein the coversequence is provided to the given receiver in response to a channelallocation request.
 7. A method as in claim 1 wherein the cover sequenceis a long pseudorandom noise (PN) code.
 8. A method as in claim 1additionally comprising the step of if frames are received out of order,requesting retransmission of missing frames at a higher levelcommunication layer.
 9. A method for communication in a time divisionmultiplex system wherein access to a shared physical channel is assignedon a demand basis by allocating timeslots to provide multipleconnections between transmitters and receivers, each given connection ofthe multiple connections having a given receiver, the method comprising:at a transmitter, allocating at least one time slot to carry forwardlink packet data on a forward link channel; dividing a given packet intoat least one frame; encoding each of said at least one frame with aforward error correction code; further encoding each of said at leastone frame with a cover sequence unique to the given connection betweenthe transmitter and the given receiver; at the given receiver,performing a cover sequence decoding process by combining a receivedsignal with a cover sequence unique to the given receiver of the givenconnection, to provide a candidate frame; decoding the candidate frameusing a forward error correction decoding process; and if the forwarderror correction decoding process indicates an erroneously receivedcandidate frame, discarding the candidate frame without passing anyerror indication to a higher level communication layer.
 10. A method asin claim 9 additionally comprising: if the forward error correctiondecoding process indicates a correctly received candidate frame, thenforwarding the candidate frame to a packet assembler process in a higherlevel communication layer.
 11. A method as in claim 9 wherein the sharedphysical channel is a wireless channel.
 12. A method as in claim 9wherein the cover sequence is provided to the given receiver during asystem configuration phase.
 13. A method as in claim 9 wherein the coversequence is provided to the given receiver in response to a channelallocation request.
 14. A method as in claim 9 wherein the coversequence is a long pseudorandom noise (PN) code.
 15. A method as inclaim 1 additionally comprising the step of: if frames are received outof order, requesting retransmission of missing frames at a higher levelcommunication layer.
 16. A system for communication in a time divisionmultiplex system wherein access to a shared physical channel is assignedon a demand basis by allocating timeslots to provide multipleconnections between transmitters and receivers, each given connection ofthe multiple connections having a given receiver, comprising: atransmitter, the given receiver having a given connection to thetransmitter, a plurality of time slots operable to carry forward linkpacket data on a forward link channel, the packet adapted to besubdivided into frames; an FEC encoder operable to encode the frameswith a forward error correction code, a cover sequence encode circuit atthe transmitter operable to further encode the frames with a coversequence unique to the given connection between the transmitter and thegiven receiver, a cover sequence decode circuit at the given receiveroperable to decode a transmitted frame by combining a received signalwith a cover sequence unique to the given receiver of the givenconnection to provide a candidate frame, an FEC decoder at the givenreceiver operable to decode the FEC code using a forward errorcorrection decoding process, the cover sequence encoding operable to bedecoded only by the cover sequence unique to the given receivercorresponding to the given connection.
 17. The system as in claim 16wherein the cover sequence decoder circuit is further operable to, inthe case of an unintended frame being received, produce a decode resultwhich will cause the FEC decoder to fail.
 18. The system as in claim 16wherein the FEC decoder is further operable to, if the forward errorcorrection decoding process indicates an erroneously received candidateframe, discard the candidate frame without passing any error indicationto a higher level communication layer.
 19. The system as in claim 16wherein the shared physical channel is a wireless channel.
 20. Thesystem as in claim 16 wherein the given receiver is further operable toobtain the cover sequence during a system configuration phase.
 21. Thesystem as in claim 16 wherein the given receiver is further operable toissue a channel allocation request in response to which a cover sequenceis provided.
 22. The system as in claim 16 wherein the cover sequence isa long pseudorandom noise (PN) code.
 23. The system as in claim 16wherein the given receiver is further operable to, if the frames arereceived out of order, request retransmission of missing frames at ahigher level communication layer.